xorl %eax, %eax

VLC SMB URI Remote Stack Buffer Overflow

with 3 comments

This vulnerability was disclosed on 24 June 2009 and affects VLC player up to 0.9.9a release (latest by now). Here is the vulnerable code as seen in modules/access/smb.c.

#ifdef WIN32
static void Win32AddConnection( access_t *p_access, char *psz_path,
                                char *psz_user, char *psz_pwd,
                                char *psz_domain )
{
    DWORD (*OurWNetAddConnection2)( LPNETRESOURCE, LPCTSTR, LPCTSTR, DWORD );
    char psz_remote[MAX_PATH], psz_server[MAX_PATH], psz_share[MAX_PATH];
        ...
    sprintf( psz_remote, "\\\\%s\\%s", psz_server, psz_share );
        ...
    FreeLibrary( hdll );
}
#endif // WIN32

As you can easily realize, this affects only Windows platform and it is a classic sprintf overflow in psz_remote which has size of MAX_PATH. An attacker can trick the victim into opening a malicous SMB share using VLC to execute arbitrary code. The patch that fixes this bug is:

    }
 
-    sprintf( psz_remote, "\\\\%s\\%s", psz_server, psz_share );
+    snprintf( psz_remote, sizeof( psz_remote ), "\\\\%s\\%s", psz_server, psz_share );
     net_resource.lpRemoteName = psz_remote;

Written by xorl

July 3, 2009 at 17:11

Posted in bugs, Windows

3 Responses

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  1. Now imagine that “\\\\%s\\%s” will result in a string exactly MAX_PATH chars long, just from looking at the patch presented here, I’d say we have some memory disclosure at least (after the patch).

    oxff

    July 4, 2009 at 12:14

  2. And there is still a truncation there, if the first string is equal to MAX_PATH, then the second one will be truncated.

    xorl

    July 6, 2009 at 16:08

  3. While the memory disclosure is true for programs built with visual studio (_snprintf from msvcrt doesn’t guarantee the null termination), that is not a problem here because vlc is built with mingw, and mingw provides its own implementation of snprintf, which is safer.

    And true, there is still a truncation.

    geal

    September 5, 2009 at 07:44


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